Ultrasound technology is conventionally used in both therapeutic and diagnostic applications. Diagnostic ultrasound generally relates to the imaging of biological tissue using an ultrasound transducer to transmit ultrasonic waves and receive ultrasonic echoes reflected from the tissue. A transducer is typically placed on the body surface or internal to a body lumen of a patient in a selected imaging region. The ultrasound transducer generates and directs ultrasonic waves to the imaging region. The transducer then receives ultrasonic waves reflected from the region and converts the received waves into electrical signals that are processed to form a diagnostic image. Typically usage of higher frequency, lower energy ultrasonic waves yields better quality images.
Therapeutic ultrasound applications include hyperthermia treatment and ultrasound-assisted administration of bioactive materials. Hyperthermia treatment comprises heating body tissues, such as tumor tissue, with focused ultrasonic waves to reduce the size or retard the growth rate of the tissue. Therapeutic ultrasound heating effects are enhanced by introduction of microbubbles into the treated tissue region.
Ultrasound-assisted administration of bioactive materials typically includes the operations of enclosing a bioactive material in vesicles, applying a quantity of the vesicles systemically to a patient, and monitoring the vesicles to determine when a suitable quantity of the vesicles are located in a region of interest. One technique for monitoring the vesicles is imaging with diagnostic ultrasound. When the vesicles are located in the region of interest, therapeutic ultrasonic waves are applied to the region of interest to rupture the vesicles and release the bioactive material, thereby attaining targeted delivery of the bioactive material or agent directly to the region of interest. Therapeutic ultrasound treatment most suitably involves application of lower frequency ultrasonic waves to attain low attenuation in contrast to the higher frequencies that are advantageous for diagnostic imaging to obtain better resolution.
One example of a combined diagnostic and therapeutic ultrasound application is disclosed in Unger et al in U.S. Pat. No. 5,558,092 in which ultrasonic imaging is performed in a region of a patient while simultaneously applying therapeutic ultrasonic waves to the region to rupture vesicles administered to that region for various purposes, such as the targeted release of a bioactive agent combined with the vesicles.
The ultrasonic transducer assembly disclosed by Unger et al. comprises a plurality of therapeutic transducer elements for generating therapeutic ultrasonic waves, and a plurality of diagnostic transducer elements for generating and/or receiving diagnostic ultrasonic waves arranged on a common platform having a substantially planar upper surface. The therapeutic transducer elements are disposed on the planar surface of the platform central to the diagnostic transducer elements. The diagnostic transducer elements are positioned outward from the centrally located therapeutic transducer elements to enlarge the field of view of the ultrasonic transducer assembly, increase imaging sensitivity and increase the image resolution.
Unger et al. proposes several transducer configurations that allow separate therapeutic ultrasound delivery and imaging. One proposed array has a two dimensional matrix of elements that is operated in a multiplexed manner such that sequential linear sets of elements are activated so that a therapeutic sector is stepped across the skin surface of the patient. The Unger et al. ultrasonic system is thus used for shallow operation near the skin surface. The linear array of therapeutic transducer elements can be operated in a continuous wave mode or in a pulse repetition frequency (PRF) mode as selected by an operator. The amount of energy supplied to the therapeutic transducer elements and the treatment depth can be controlled by the operator.
The multiplexed, two-dimensional array disclosed by Unger et al. insonifies tissue focused at a particular depth both for diagnostic and therapeutic purposes. In one embodiment, an external transducer array contacts the skin to image and deliver therapy to a plane of tissue just below the skin. In another embodiment, an intracavitary probe incorporates a transducer assembly that encircles the probe shaft just below the tip for usage in either endovaginal or endorectal imaging for therapeutic and diagnostic usage focused in a curved plane of tissue enclosing and adjacent to the imaged cavity.
Several problems reduce the utility of conventional systems that combine diagnostic and therapeutic ultrasound application. For example, diagnostic ultrasonic energy is applied near the imaging surface while many therapeutic procedures should apply energy to deep tissue. Also, the ultrasonic energy for therapeutic application is focused at a particular tissue depth with substantial attenuation as the depth increases. A more effective therapy would deliver an essentially uniform energy throughout a range of depths. Furthermore, conventional systems form two-dimensional images of tissue masses that typically have a three-dimensional structure.
What is needed is a combined diagnostic and therapeutic ultrasound system that images and delivers therapy to a volume of tissue.
A fully steerable two-dimensional ultrasound array performs simultaneous diagnostic imaging and delivery of a therapy by beam forming and steering by selective focusing of beams. In one example, the two-dimensional ultrasound array includes a controller that controls beam forming and focusing to scan the focal point of the beam in a pattern within an identified structure of a image. Tissue is thus scanned using a sharply focused beam that is suitable for delivering a therapy such as hyperthermia therapy or delivery of a pharmaceutical via microspheres. Imaging and therapy proceed either simultaneously or separately by operator selection. In one mode of operation, simultaneous operation of imaging and therapy delivery is attained using a focused, scanned beam in which a focused beam, that delivers intensity levels suitable for heating tissue or for bursting microspheres, is pulsed. Reflected signals from the pulses are detected and used to create an image in the manner of conventional ultrasound imaging.
In an alternative mode of operation, therapy is delivered in a continuous-wave mode to gradually heat tissue, burst microspheres, or otherwise stimulate pharmaceutical action. Ultrasound pulses are interspersed with the continuous-wave signal to interrogate the tissue for image formation.
Alternatively, the controller is capable of controlling beam forming and focusing to defocus the beam to match the cross-sectional size of the tissue-of-interest and directing the resulting broad beam at the tissue-of-interest. The broad beam is defocused to have relatively uniform insonation.
A fully steerable two-dimensional ultrasound array performs simultaneous diagnostic imaging and therapy by exploiting the scanning capability of a two-dimensional array. Ultrasonic beams are sharply focused to generate intensity levels that are suitable for heating tissues in a hyperthermia application and for bursting microspheres in a therapy utilizing microsphere-encased pharmaceuticals. The sharply focused echoes are delivered in pulses and reflections from the pulses are detected and used to create an ultrasound image.
A fully steerable two-dimensional ultrasound array performs imaging and delivery of a therapy by beam forming and steering so that a plurality of elements in the array are active simultaneously. The individual elements in the array are activated and relatively delayed so that a resultant ultrasonic beam is formed and directed in a controlled direction with a focal point set at a desired depth. The ultrasonic beam is controlled to direct the beam in a selected direction within a hemisphere having an origin at the face of the transducer. The phased and steerable two-dimensional array delivers ultrasound energy to a volume within a body.
In one application, a two-dimensional array of ultrasonic transducer elements are individually excitable for both imaging and delivery of ultrasonic energy to a three-dimensional volume of tissue. In some embodiments, the pitch of the elements in the array is preferably no greater than one-half the acoustic wavelength of the interrogation signal to form a clean, focused beam with low side-lobe levels.
The pattern of activated elements and relative timing of the elements are controlled to change the size of the transducer aperture, thereby controlling the depth of focus along an interrogation axis of the interrogation volume. The transducer elements can be activated in various selected patterns to determine the size, shape, and position of the insonated volume. The pattern of activated transducer elements can be translated to move the interrogation axis off-center.